The Algorithm On Multi-secondary Controlling Acoustic Sources For Instabilities And Noise Of Combustion
- Paper number
IAC-07-C4.I.15
- Author
Mr. Fei Dong, Northwestern Polytechnical University, China
- Year
2007
- Abstract
In the research on actively controlling unstable combustion and the burning noise, establishing more reasonable physical model and more easily solved mathematical model, since long ago, has been the critical problem. However, no literature about unstable combustion has been involved about the algorithm using the principle of smallest sound potential energy in the entire burning field to design secondary controlling sources. Therefore, based on the sound potential energy smallest principle, this article conducts the research about establishing model of multi-secondary controlling acoustic sources in the view of the acoustics characteristic of burning noise and unstable combustion. The main researching idea is to simplify source terms of sound wave equation in the combustion field, and to regard the combustion field as a collection of the multitudinous spot acoustic sources. Then based on smallest sound potential energy principle in whole combustion field, to determine the plural intensity of secondary acoustic source as controlling input, finally to calculate the best noise reduction quantity after the secondary acoustic sources are added to implement control. In computation process, all are regarded as the secondary acoustic source, regardless of using the speakers or secondary pulsation fuel sprays as controlling sources. Algorithm on multi-secondary controlling acoustic sources for instabilities and noise of combustion will in detail be introduced from followed aspects. The liquid fuel and the oxidant are gushed into the combustion chamber through the spraying and atomizing nozzle to mix and to burn. The combustion field is made of two components including the fluid and gas. From its equations of the continuity, momentum and energy, we may deduce the sound wave equation in combustion field. It is supposed the sound wave equation in seal combustion field may be expressed by a series of added sound modes. Sound pressure in any spatial position may be deduced. In order to achieve the goal of suppressing noise, we should make the sound potential energy in the entire space become the smallest. The solution of equation above may results in the optimizing strength of controlling source of sound and the optimal noise reduction quantity. According to the combustion theory in which majority of the burning noise comes from the outside-flame, the sound source caused by burning may approximately be thought as a face of acoustic source of the outside-flame surface composed by the multitudinous spot acoustic sources, so total intensity of sound source in the combination field is easily obtained. Finally, an ideal effect has been obtained in a case using above algorithm in controlling unstable combustion and noise.
- Abstract document